In a vehicular hybrid drive unit, an internal combustion engine such as a gasoline engine or a Diesel engine and an electric device such as a motor generator are generally used as prime movers. The modes of combination of those internal combustion engine and electric device are various, and the number of electric devices to be used is not limited to one but may be plural. In JP-A-2002-225578, for example, there is described the hybrid drive unit, in which an engine and a first motor generator are connected to each other through a synthesizing/distributing mechanism composed of a single pinion type planetary gear mechanism so that a torque is transmitted from the synthesizing/distributing mechanism to an output member, and in which a second motor generator is connected to the output member through a gear shift mechanism so that the output torque of the second motor generator is added as the so-called “assist torque” to the output member. Moreover, the gear shift mechanism is constructed of a planetary gear mechanism capable of being interchanged between two stages of high and low, i.e., a directly connected state and a decelerating state. In the directly connected state, the torque of the second motor generator is applied as it is to the output member. In the decelerating state, on the other hand, the torque of the second motor generator is raised and applied to the output member.
In the aforementioned hybrid drive unit, the second motor generator is controlled into a power mode or a regenerative mode so that a positive torque or a negative torque can be applied to the output member. Moreover, a deceleration state can be set by the transmission so that the second motor generator can be changed into a low torque type or a small size type.
Here, in JP-A-2000-295709, there is described a device, in which first and second motor generators are arranged on the upstream side (or the engine side) of a transmission capable of being switched to high and low modes, so that the gear shifting time may be made substantially constant by controlling the torques of the individual motor generators at the shifting time of the transmission.
When a gear shift of that device is executed by a claw clutch, an additional torque corresponding to a dragging torque is determined and is applied by the electric motor so that the speed of the clutch may quickly reach a synchronous speed.
In JP-A-6-319210, on the other hand, there is described a device, in which the output torque of an engine is transmitted to a predetermined input member of a transmission, and a motor generator is connected to the input member so that the motor generator is controlled to smoothen the output torque, i.e., to absorb an inertial torque at a shifting time.
In Japanese Patent No. 2926959, moreover, there is described a device, in which the output of a power generating source is changed into a drive state or a driven state, when the drive state or the driven state cannot be clearly decided, and a gear shift is then executed.
In JP-A-6-319210, moreover, there is described a device, in which a motor torque is lowered at an inertia phase or at its final stage to absorb an inertia torque so as to reduce the shocks at the shifting time of a transmission assembled in a hybrid drive unit.
In JP-A-9-32237, on the other hand, there is disclosed a hybrid drive unit having a transmission, in which the initial oil pressure of a frictional engagement device to participate in the gear shift of the transmission is learned on the basis of a torque correction amount of a motor for inputting a torque to the transmission.
According to the device described in JP-A-2002-225578, the torque outputted from the main prime mover composed of the engine and the first motor generator is transmitted to the output member, whereas the torque outputted from the second motor generator can be transmitted to the output member. Therefore, the engine constructing the main prime mover is run for the optimum fuel consumption so that the short or excessive torque for the drive force demanded in that state can be supplemented by the second motor generator. Moreover, the device is provided with the transmission so that the torque of the second motor generator can be raised and transmitted to the output member. As a result, the second motor generator can be made to have a small size or a low capacity.
The aforementioned device has such advantages, but shocks may occur in case the gear shifting operation is done by the transmission. Specifically, the rotating speed of any rotary member is changed by the gear shift so that an inertia torque is established by the change in the rotating speed and affects the output torque. This change in the output torque may appear as the shocks. In case the gear shift is executed by applying or releasing the frictional engagement device, moreover, the torque capacity of the frictional engagement device transiently lowers to restrict the torque which can be assisted by the second motor generator. As a result, the entire output torque of the hybrid drive unit or the drive torque of the vehicle may change during the gear shift thereby to cause the shocks.
On the other hand, the transmission in the hybrid drive unit, as described in JP-A-2002-225578, is constructed to shift the gears at two stages of low (or low gear stage) and high (or direct stage) stages by a brake and clutch. At the shifting time, therefore, one of the brake and the clutch is released whereas the other is applied so that both have to be coordinately controlled. This control has a tendency to elongate the time period necessary for the gear shift. During this gear shift, moreover, the transmission torque capacity by the transmission is reduced. Therefore, the fall in the output shaft torque may be deepened not only by that reduced torque capacity but also by the long shifting time period.
In the aforementioned device described in JP-A-2002-225578, in the gear shift of the case where the so-called “torque assist” is done by the second motor generator, for example, the torque capacity in the transmission, i.e., the torque capacity of the frictional engagement device to participate in the gear shift exerts influences on the output shaft torque. In case the torque to be transmitted from the internal combustion engine to the output shaft by controlling the first motor generator is controlled at the shifting time, moreover, it is necessary to control the torque of the first motor generator according to the torque capacity in the transmission.
However, the relation between the apply pressure and the torque capacity of the frictional engagement device such as the clutch or the brake is not constant due to the individual difference or the aging so that the torque to appear on the output shaft at the shifting time may become different from the expected one to deteriorate the shocks. In case the so-called “torque assist” at the shifting time is done by the electric motor such as the motor generator in the hybrid drive unit, on the other hand, the torque of the electric motor may become different from the needed one. As a result, the output shaft torque may become short or excessive to cause the shocks.
The aforementioned invention, as described in JP-A-9-32237, is constructed such that the advancing velocity of the gear shift is controlled by the motor torque so that the initial apply pressure is learned on the basis of the motor torque. Therefore, it is possible to learn the initial apply pressure for optimizing the change in the speed at the shifting time, but it is impossible to precisely determine the relation between the torque capacity and the apply pressure of the frictional engagement device to participate in the gear shift.